Vehicle parking brake system

ABSTRACT

A parking brake system for vehicles, in particular passenger cars, with an extraneous force generating adjusting unit for tightening or loosening at least one actuating pull for a braking arrangement on the vehicle and having an electronic control device whose output variable is used to actuate the adjusting unit. Input variables, in particular from an operating arrangement, sensors and or switches are fed to the control device and the output variable van be varied as a function of the input variable. A force sensor is disposed on or the actuating pull for directly detecting the force exerted thereon. The signals from the force sensor are fed to the control device as an input variable.

BACKGROUND OF THE INVENTION

The invention relates to a parking brake system for vehicles, inparticular passenger cars, having a power-assistance-generating actuatorunit for pulling on or releasing at least one control cable for abraking device of the vehicle, having an electronic control device whoseoutput variable is used to activate the actuator unit, the controldevice being supplied with input variables, in particular from anoperator device, from sensors and/or switches or the like, and it beingpossible to change the output variable as a function of the inputvariable.

DESCRIPTION OF THE RELATED ART

DE 42 05 590 A1 has already disclosed such a parking brake system formotor vehicles with a foot-activated brake pedal. Here, an additionalelectromotive actuator unit which acts directly on the brake pedal via acoupling device is provided. By pressing a momentary contact switchwhich is located, for example, in the operating reach of the vehiclegear mechanism, the direction of rotation of the electric motor of theactuator unit is reversed in each case so that the brake pedal ispivoted downward electromotively and released upward again. Themechanical arresting of the brake pedal is carried out here by means ofthe actuator unit gear mechanism which is of self-locking design.Furthermore, the design of the coupling device permits the brake pedalto be pressed down by the operator at any time. The parking brake systemhas an electronic control device with which additional functions can beimplemented. Thus, for example the power-assisted parking brake systemcan be protected against unintentional release by virtue of the factthat after the ignition is switched off the actuator unit is no longeractuated electrically. Also, the detection of the operating current ofthe electric motor, and the detection of the angle of rotation of thespur gear of the gear mechanism can provide an indication of the brakingforce and the instantaneous position on the travel path of the brakecable, from which indications of the state of the friction linings ofthe parking brake system and the state of the braking force-transmittingconnecting elements can be obtained. Furthermore, the braking force canalso be applied under the control of a characteristic diagram by meansof the operating current of the electric motor, in which case anactivation speed which is dependent on the travel of the brake cable canalso be implemented.

However, the known parking brake system proves disadvantageous insofaras it is extremely inflexible in its handling and takes little account,or no account at all, of the individual load states of the control cableand/or of the braking device. Furthermore, it proves disadvantageousthat the activation force which acts on the control cable and/or on thebrake takes place indirectly via a measurement of the current flowinginto the electric motor of the actuator unit. On the one hand, thismeasurement method is extremely imprecise since the current flowing intothe electric motor of the actuator unit is also dependent onenvironmental influences such as temperature or the like. On the otherhand, it is, at any rate, then impossible to measure a force if theelectric motor is out of operation.

Furthermore, JP-A-5-286424 has disclosed a parking brake for motorvehicles in which, after an activation lever is pulled on by the driver,a pressure sensor detects the reaction force of the parking brake whichis exerted on a sliding element. In the event of the reaction forcewhich is measured being smaller than a predefined value, an actuatormotor is driven in the forward direction with the aid of a controller,the activation lever being raised, together with the sliding element, bymeans of a cable line. As a result, the intention is that the brakecable will continue to be pulled and the effective force on the parkingbrake will be increased. As soon as the pressure sensor detects that theactivation force has reached a predefined value, the motor is stopped,the activation lever being held in the raised position. A disadvantagewith the known system is that the force exerted on the control cable isnot directly detected so that the measurement may be subject toconsiderable errors.

SUMMARY OF THE INVENTION

In contrast to the above, the invention is based on the object ofdeveloping a parking brake system for vehicles with the featuresmentioned at the beginning to the effect that flexible handling isensured and the individual load states of the parking brake system canbe detected reliably and precisely.

This object is essentially achieved according to the invention with theparking brake system having the features mentioned at the beginning inthat a force sensor for directly detecting the force which is exerted onthe control cable is arranged on or in the control cable, the signals ofthe force sensor being supplied to the control device as an inputvariable.

The actuation movement of the power-assistance-generating actuator unitis converted into a translatory movement for activating or pulling on orreleasing the control cable for a braking device. A force sensor whichdirectly measures the force acting on the brake line or the brake andpasses on this force as an actual value to the control device isarranged on or in the control cable. In particular, with the parkingbrake system according to the invention it is also possible to measure aforce directly when the vehicle is stationary so that continuousmonitoring of the braking force at a given moment is made possiblewithout the power-assistance-generating actuator unit having to be inoperation. This is not possible with the parking brake system accordingto the prior art. In this way, the parking brake system according to theinvention can be automatically re-adjusted if there is any kind offailure of the braking force, even if the vehicle has been parked in thedeactivated state for a relatively long time.

According to a first advantageous refinement of the invention there isprovision for the dynamometer to have an elastic element which isarranged on or in the control cable and whose deformation, for exampleits expansion or torsion, is used to determine the force exerted on thecontrol cable. This makes it possible, in a structurally simple way, tosense the force on the control cable directly. A spring, for example, ispossible as the elastic element, said spring being integrated into thecontrol cable or being coupled, at one end of the line, in articulatedfashion with respect to the signal transmitter or pickup unit. Bysensing the spring travel it is then possible to draw conclusions aboutthe corresponding force.

According to a further advantageous refinement of the invention there isprovision for the control cable to be assigned a displacement sensor forsensing the travel of the control cable, the signals of which sensor aresupplied to the control device as an input variable. In this way, thetravel or adjustment displacement can be sensed by means of thedisplacement sensor both when pulling on and releasing the brake or thecontrol cable, and can be used, if appropriate, for evaluating thebraking characteristics and for possible fault diagnostics. A furtheradvantage is that an additional position detection, by means of limitswitches or the like is not necessary as a result of the use of thedisplacement sensor.

In this context, according to a further development of the invention, itis possible for the control device to have a memory device and acomparator, at least value pairs, “travel of the control cable/forceacting on the control cable” being stored as reference values in thememory device and the reference values being compared with theinstantaneous values and/or actual values in the comparator. Forexample, the position of the control cable which has been determined bythe displacement sensor can be assigned the corresponding output valueof the force sensor, all the data of a braking procedure being stored inthe memory device. When there is further parking brake procedure, thesestored data are used as reference values. If there are deviationsbetween the measured values (actual values) and the reference values(setpoint values) it is then possible to conclude that the parking brakesystem is not operating correctly.

According to a further embodiment of the invention, a signaling devicecan be activated by the comparator if the reference values andinstantaneous values have deviations from one another which are above atolerance threshold.

Furthermore, it is possible for the reference values which are stored inthe memory device to be updated or adjusted adaptively so thatcontinuous or long-term changes in the brake system are taken intoaccount in the reference values. As a result, the reference values canbe adapted, for example to the setting behavior of the overall system,wear of the brake linings, lengthening of the control cables or thelike. This provides a considerably improved diagnostics capability ofthe parking brake system according to the invention.

Furthermore, one advantageous refinement of the invention provides thepossibility for the control device to be supplied, as an input variable,with signals for the force which is to be exerted on the control cable,a force pickup which is coupled to the brake pedal of the vehiclepreferably being used as the setpoint value signal transmitter. However,it is also possible for customary electronic operator elements, such apotentiometers, switches, rocker switches, momentary-contact switches orthe like, which may be arranged at any location within reach of thedriver, to be used as setpoint value signal transmitter. Likewise, it isconceivable to implement the braking force setpoint value by means of aforce sensor which is integrated in the brake pedal and which detectsthe activation force of the brake pedal by the driver and passes it onto the control device. The actual braking procedure is then triggeredeither automatically, for example when the vehicle comes to astandstill, or by means of a control device, or an activation elementsuch as a switch, rocker switch or the like, being activated. This ispossible both when the vehicle is stationary, that is to say for examplewhen it is parked, and when traveling if the parking brake system is tobe used as an auxiliary brake, for example when the main brake fails.

Alternatively, it is possible for the control device to be supplied, asan input variable, with signals of an inclination sensor. As a result,the braking force of the parking brake system can be prescribed, as asetpoint value, as a function of the inclination of the vehicle, as aresult of which it is ensured that there is optimum adaptation to therespectively required braking force. The actual braking procedure isthen either cleared automatically when the vehicle is stationary or elseas a result of the control device being activated or the ignition or thelike being switched off. Of course, this prescription of the setpointvalue of the inclination sensor can be switched off by furtheractivation of the control element and the braking force can be set, forexample, to a maximum value.

Furthermore, it has proven advantageous for the actuator unit to bedesigned as a d.c. motor with a connected or integrated gear mechanism.

According to another advantageous development of the invention, thetravel value of the control cable which is necessary to exert apredetermined maximum force value is stored in a memory device while thebrake is being pulled on, the control cable being displaced by thisstored, preferably constant, travel value by means of the actuator unitin order to release the brake. On the basis of these measures it ispossible to carry out automatic length compensation of the controlcable. If, for example when the parking brake is pulled on, the controlcable has lengthened by a certain value, for example 0.5 mm, thislengthening is removed from the system by virtue of the fact that, inorder to release it, the control cable is merely displaced by the amountof travel previously necessary to load it. As a result, the zero pointof the system is displaced by the amount of lengthening of the cable sothat the slack is removed from the system. Of course, the brake can alsobe released by force control.

According to a further refinement of the invention, a display device,such as a visual display, for example an LED array, or an audibleindicator, with which the instantaneous braking force can berepresented, is connected to an output of the control device.

Furthermore, the control device can advantageously be designed as adigital signal transmitter or else a multistep or stepless signaltransmitter downstream of a servocontroller. In either a stepped orstepless operating mode, metered pulling on and releasing of the parkingbrake system can be achieved, which is also advantageous when theparking brake system is used as an auxiliary braking device, for examplein the event that the main brake system has failed. The elimination of amechanical activation device and the use of the electrical operatordevice makes it possible, as a further advantage, to make a considerablesaving in space and to arrange the electrical operator device asdesired, since said device does not need to be coupled to the mechanicaloperator element of the parking brake system. In addition, it is nolonger necessary to apply force to activate the parking brake system.

The servocontrol can be provided in the following ways:

by means of pulse-width modulation (PWM),

by controlling the amplitude of the voltage of the motor,

by means of clocked motor voltage with constant mark-to-space ratio,

by means of on-off operation, for example switching on the motor whenthe setpoint value changes and switching it off when the actual valueand setpoint value correspond.

Of course, the operator device can also be designed as a mechanicalcontrol element for pulling on or releasing the control cable.

According to another particularly advantageous embodiment it is possiblefor an auxiliary braking device to be provided for switching over theparking brake into an auxiliary braking mode in the event of the servicebrake system failing, the brake pedal having a force pickup as asetpoint value signal transmitter for the parking brake.

In conjunction with a dual-function pedal it is possible to performemergency activation of the parking brake system so that additionalmechanical activation devices, such as hand brake lever or an additionalpedal can be dispensed with. Such a dual function of a pedal isdescribed in more detail in the patent application 197 26 188.4, saiddual function being included, by express reference, in the disclosuresof the earlier application. The emergency activation of the electricparking brake may be designed not only as a mechanical version, forexample double pedal, but also as an electrical version by using anadditional control unit and, if appropriate, an additional actuator unit(motor with gear mechanism) and possibly an additional battery.

It is also possible for the control device to be supplied, as inputvariable, with at least one or more of the following signals: signalfrom the ignition switch, signal from the immobilizer device, signalfrom the speedometer, signal from a brake light switch, signals from theantilock brake system, signals from a door lock contact, signals from adiagnostics device. Various refinements of the parking brake system arepossible on the basis of these measures. For example, a safety positionmay be implemented, for example, as a child safety system, by virtue ofthe fact that the parking brake system or the operator device can beactivated in particular only when the ignition is switched on or the keyis in the ignition lock, or the parking brake system or the operatordevice is coupled to the immobilizer device. As a result, a certainlevel of protection against theft is also provided. Of course, theparking brake system can be pulled on at any time, irrespective of theposition of the ignition lock.

However, in this context it is also possible that, if appropriate, thevehicle speed is additionally sensed in order to distinguish between thevehicle traveling and the vehicle being stationary, so as to distinguishbetween the sparking “braking” and “auxiliary braking” modes ofoperation, for example in the event of the service brake system of thevehicle failing.

Also, the activation of the brake pedal can be logically linked orcoupled, for example via a brake light switch, to the actual controldevice so that unintentional activation of the parking braking devicewhile traveling can be avoided or prevented if the control devicehappens to be inadvertently activated. In this context it is alsopossible for a visual or audible warning signal to be issued initiallywhen unintentional activation takes place, without the parking brakeprocess having been activated. This could then take place, for example,when the control element is activated once more. Also, the parking brakesystem can be released automatically and/or an audible signal can beissued when a journey is started if the parking brake has not beenreleased before the journey begins. The criterion for this can bederived, for example, from the speed sensor, it being then necessary tomake a distinction between the states of the vehicle in which the speedis zero and those in which the speed is greater than zero. By virtue ofthe fact that the control device is also provided with signals from theantilock brake system, it is possible to avoid overbraking in certainsituations by means of the parking brake system. Furthermore, it is alsopossible to provide a visual display which indicates, for example bymeans of a signaling light or the like, that the predefined brakingforce has been reached.

The parking brake system according to the invention also permits anextensive diagnostics capability by virtue of the sensing of theadjustment displacement of the control cable and the force acting onthis control cable. In this way it is possible, for example, to detectreadily a defect in the actuator unit, the sensor system, the activationmeans or even to detect a rupture in the control cable. In order todetect faults and limit the current the motor current is measured or theduration of a braking procedure is determined. However, it is alsopossible to predefine a time window in which the braking procedure mustbe terminated.

According to a further refinement it is possible for the parking brakesystem to be changed automatically into the auxiliary braking mode bythe auxiliary braking device when a fault is diagnosed in the servicebrake system of the vehicle. If a defect in the actual service brake isdetected by the diagnostics device, an auxiliary braking operation canbe carried out automatically using the parking brake system according tothe invention by activating the brake pedal. This can be implemented inparticular by using a force sensor, which is arranged or integrated inor on the brake pedal, to determine the activation force acting on thepedal. During the automatic switching over to the electrical parkingbrake system, it is of course also possible to process the influences ofthe antilock brake system when the desired braking effect is achieved.The advantage is that time is not wasted on thinking about changeover(reaction time).

It is also possible for the force which is exerted on the control cableby the actuator unit to be limited to an upper limiting value by meansof a limiting device. In this way, by using the force sensor, it ispossible to limit the force acting on the control cable or the brake, inorder to avoid overstressing the control cable. As a result, the parkingbrake system according to the invention is further improved as a safetypromoting component in its function over and beyond the customary safetystandard. It goes without saying that this measure also furtherlengthens the service life of the control cable between the signaltransmitter and the pickup.

Further objectives, advantages, features and application possibilitiesof the present invention emerge from the following description of theexemplary embodiment with reference to the drawings. Here, all thedescribed and/or illustrated features form, either independently or inany desired appropriate combination, the subject-matter of the presentinvention, even independently of their combination in the claims ortheir backward reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of an exemplary embodiment of the parkingbrake system according to the invention,

FIG. 2 shows an exemplary embodiment of a block circuit diagram of thecontrol device for the parking brake system according to the invention,

FIG. 3 shows an exemplary structogram or flowchart of the method ofoperation of the electronic control device which can be implemented bymeans of a microcontroller, for example, and

FIG. 4 shows a further structogram or flowchart of a further exemplaryembodiment of the electronic control device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As is clear from FIG. 1 the parking brake system 10 has apower-assistance-generating actuator unit 12 for pulling on or releasingat least one control cable 14 for a braking device 16 of a vehicle, inparticular of a motor vehicle. An electronic control device 18 is usedto activate the actuator unit 12, it being possible to supply thecontrol device 18 with input variables, in particular from an operatorunit 20 and to a force sensor 22. The output variable of the controldevice 18 can be changed as a function of the input variables. The forcesensor 22 is assigned to the control cable 14 and directly senses theforce exerted on the control cable 14 by means of the actuator unit 12.The signals from the force sensor 22 are fed, as an input variable, tothe control device 18.

The force sensor 22, or the dynamometer, preferably has an elasticelement whose deformation, in particular whose expansion or torsion, isused to determine the force on the control cable 14. In particular aspring is suitable as the elastic element.

The operator unit 20 can be designed as an electrical signal transmitter40 or else as a mechanical operator element 42 for releasing and pullingon the parking brake system 10. The actuator unit primarily 12 iscomposed of a d.c. electric motor to which a gear mechanism 36 isconnected. The operator unit 20 can be activated, for example manually,by the driver of the vehicle in order to control the parking brakesystem 10. A mechanical emergency activation of the parking brake system10 can be carried out by means of a pedal 44 or the like. The parkingbrake system 10 can be pulled on or released by means of the operatordevice 20. In addition, or as an alternative, a signal transmitter 40,with which the setpoint value for the brake force which is to be set bythe actuator unit 12 can be input, is provided. The signal transmitter40 and the operator unit 20 can, for example, also be integrated in theoperator element 42. The emergency activation is thus a standby functionof the electric parking brake.

Furthermore, the control cable 14 is assigned a displacement sensor 24for sensing the travel of the control cable 14, the signals of whichsensor are fed, as an input variable, to the control device 10, as isclear in particular from FIG. 2. The control device 18 has a memorydevice 26 and a comparator 28, data or pairs of data items relating tothe “travel” of the control cable 14 and the force acting on the controlcable 14 being stored as reference values or setpoint values in thememory device 26 and the reference values being compared with theinstantaneous values in the comparator 28. If the reference values andinstantaneous values relating to the travel or the force have deviationsfrom one another which are above a tolerance threshold, a signalingdevice 30 can be activated by the comparator 28. It is also possible toupdate or adaptively adjust the reference values stored in the memorydevice 26, so that continuous or longterm changes in the brake systemare taken into account in the reference values.

The control device 18 is supplied, as an input variable, with signalsfor the force which is to be exerted on the control cable as setpointvalues, a force pickup 32 or a potentiometer, rocker or the like whichis coupled to the brake pedal of the vehicle is used as the setpointvalve sensor. Furthermore, the control device 18 can be supplied, as aninput variable, with signals of an inclination sensor 34 so that thesetpoint value of the force or braking force which is to be exerted onthe control cable 14 can be dependent on the position of the vehicle.That travel value of the control cable 14 which is necessary to exert aforce value which does not correspond to the maximum force is stored,while the brake or control cable 14 is being pulled on by means of theactuator unit 12, in a memory device 26 so that the control cable 14 isdisplaced by the stored travel value by means of the actuator unit 12 inorder to release the brake.

A display device 38, for example an LED array or an audible indicatorwith which the instantaneous braking force can be represented, isconnected to an output of the control device 18.

The operator device 20 can be designed, for example, as a multistage,stageless or digital signal transmitter 40. Of course, it is alsopossible for the operator device 20 to be stored as a mechanicaloperator element 42 is designed merely for pulling on or releasing thecontrol cable 14.

In the event of the service brake of the vehicle failing, a brakingdevice is provided for switching over the parking brake into anauxiliary braking mode, the brake pedal having a force pickup 32 assetpoint value signal transmitter for the parking brake. The controldevice 18 can be fed, as further input variables, with one or more ofthe following signals: signal from the ignition switch 48, signal fromthe immobilizer 50, signal from the speedometer 52, signal from thebrake light switch 54, signal from the antilock brake system 56, signalsfrom a door lock contact 58 or else signals from a diagnostic device 60.In the event of a fault being diagnosed in the service brake system ofthe vehicle, it is then possible to change the parking brake system 10to be changed automatically into the auxiliary braking mode by theauxiliary braking device. Finally, the force which is exerted on thecontrol cable 14 by the actuator unit 12 can be limited to an upperlimiting value by means of a limiting device 62.

According to the structogram or flowchart of a possible configuration ofthe control device 18 which is illustrated in FIG. 3, it is initiallydetermined whether activation of the parking brake system 10 isrequested by means of the operator device 20. If this is the case, it istested whether the parking brake system 10 is to be pulled on orreleased, and initially a desired setpoint value, for example for thebraking force, or else the travel of the control cable 14 is detected ineach case. The actuator unit 12 is then correspondingly activated,specifically until the detected actual value, by means of the forcesensor 22, the displacement sensor 24 or other sensors, corresponds tothe setpoint value. As soon as the setpoint value has been reached, theactuator unit 12 or the motor is switched off. If the setpoint value hasnot yet been reached, the actuator unit 12 is left in the switched-onstate, the instantaneous actual value, for example of the braking forceor of the displacement travel of the control cable is measured, comparedwith the respectively recorded setpoint value and checked forcorrespondence. If correspondence between the setpoint value and actualvalue is not achieved, the actuator unit is switched off again.

According to the structogram or flowchart of a further possibleconfiguration of the control device 18 which is given in FIG. 4, it isinitially detected whether activation of the parking brake system 10 isrequested by means of the operator system 20. If this is the case it istested whether the parking brake system 10 is to be pulled on orreleased, and initially a desired setpoint value, for example for thebraking force, or else the travel of the control cable 14 is detected ineach case. Then the corresponding actual value is determined and it istested whether the desired setpoint value has been reached. If this isnot the case, an error signal is determined, for example, from thesetpoint value and actual value, and therefrom a manipulated variable,for example a pulse width-modulated signal, a control voltage or a clocksignal, with which the servocontrol of the actuator unit is performed,is obtained from said signal. The actuator unit 12 is thencorrespondingly activated, specifically until the detected actual value,by means of the force sensor 22, the displacement sensor 24 or othersensors, corresponds to the setpoint value. As soon as the setpointvalue has been reached, the actuator unit 12 or the motor is switchedoff. If the setpoint value has not yet been reached, the actuator unit13 is left in the switched-on state, the instantaneous actual value, forexample of the braking force or of the displacement travel of thecontrol cable is measured, compared with the respectively detectedsetpoint value and checked for correspondence. In this context, themanipulated variable is newly calculated for each pass through thecontrol loop. Once correspondence between the setpoint value and actualvalue has been achieved, the actuator unit is switched off again.

Basically two input variables are necessary to activate the parkingbrake. These input variables are generated by the triggering device andthe setpoint value specifying system. While the triggering device isdesigned as a momentary-contact switch, switch, brake light contact,rocker or the like, the setpoint values are specified by means of apotentiometer, an inclination sensor, force pickup in the brake pedal orthe like. The triggering device and setpoint value specifying system canbe implemented separately, for example as a push-button key andinclination sensor, or else together by means of an operator element,for example potentiometer.

Basically three types of electric parking brakes can be provided:

In the case of a digital parking brake, the brake is set to a prescribedmaximum force which cannot be changed by the driver. The electricparking brake is released by a prescribed amount of displacement whichcannot be changed by the driver either and which is either determined inan initialization routine or permanently prescribed as a constant in anonvolatile memory. However, this is only possible if the abovementionednonvariable maximum force has been set. The compensation of length isperformed in this way.

However, if the brake is released before this force is reached, thedisplacement which has been measured until then for the respectivepulling on of the brake is used to release it. There is no compensationof length here. A triggering device (momentary-contact switch, switch orthe like) is sufficient as the operating element because the setpointvalue is of course permanently prescribed.

In the case of the stepless electric parking brake (servocontrolled),the brake is pulled on to a force which is prescribed by the setpointvalue transmitter. The brake is released by the permanently prescribedamount of displacement (see digital electric parking brake) when thesetpoint value corresponds to the maximum force. The compensation oflength is carried out in this way. In all other cases, the brakeexperiences the amount of displacement which is measured during therespective pulling on of the brake. A triggering device and a setpointvalue transmitter are required to operate it.

A stepped electric parking brake (servocontrolled) is similar to thestepless version, but it has coarser gradation of the possible brakingforces.

The emergency activation is the standby function of the electric parkingbrake, not of the service brake. This function may be of purelymechanical design (double-function pedal) or else be a second electricparking brake.

The force pickup in the brake pedal is used to detect the activationforce of the driver applied to the brake pedal and is used as a setpointvalue specifying system. This does not correspond to the pedal having adouble function, nor is it provided for the clutch pedal.

A compensation of length is carried out by releasing the brake by aconstant amount of displacement but only if the electric parking brakehas been pulled on to the maximum force. This constant displacement iseither determined in an initialization routine and then no longerchanged or is already stored in a nonvolatile memory (EPROM, EEPROM)before the vehicle is put into service.

Key for FIG. 3

1=Motor off

2=Activation

3=No

4=Yes

5=Pull on

6=Release

7=Pull on or release brake?

8=Detect setpoint value

9=Setpoint value reached?

10=Switch on motor in direction of pulling on

11=Measure actual value (braking force, displacement travel etc.)

12=Detect setpoint value

13=Setpoint value reached?

14=Switch on motor in direction of release

15=Measure actual value (braking force, displacement travel etc.)

REPLACEMENT SHEET (RULE 26)

Key for FIG. 4

1=Motor off

2=Activation

3=No

4=Yes

5=Pull on

6=Release

7=Pull on or release brake?

8=Detect setpoint value

9=Detect actual value

10=Setpoint value reached?

11=Determine error signal, calculate manipulated variable.

12=Switch on motor in the direction of pulling on

13=Detect setpoint value

14=Detect actual value

15=Setpoint value reached?

16=Determine error signal, calculate manipulated variable

17=Switch on motor in direction of release

REPLACEMENT SHEET (RULE 26)

What is claimed is:
 1. A parking brake system (10) for vehicles, havinga power assistance generating actuator unit (12) for pulling orreleasing at least one control cable (14) for a braking device (16) ofthe vehicle, having an electronic control device (18) whose outputvariable is used to activate the actuator unit (12), the control device(18) being supplied with input variables, in particular from an operatordevice (20), from sensors and/or switches or the like, and it beingpossible to change the output variable as a function of the inputvariable, wherein a force sensor (22) for directly sensing the forceexerted on the control cable (14) is arranged on or in the control cable(14), the signals of the force sensor (22) being supplied to the controldevice (18) as an input variable, wherein the control cable (14) isassigned a displacement sensor (24) for sensing the travel of thecontrol cable (14), the signals of which sensor (24) are supplied to thecontrol device (18) as an input variable and the control device (18) hasa memory device (26) and a comparator (28), one of at least pairs ofvalues and pairs of data items being stored as reference values in thememory device (26) and the reference values being compared with thecurrent values in the comparator (28).
 2. The parking brake system asclaimed in claim 1, wherein the force sensor (22) has an elastic elementwhich is arranged on or in the control cable (14) and whose deformationis used to determine the force exerted on the control cable (14).
 3. Theparking brake system as claimed in claim 1, wherein a signaling device(30) can be activated by the comparator (28) if the reference values andinstantaneous values have deviations from one another which lie above atolerance threshold.
 4. The parking brake system as claimed in claim 3,wherein the reference values stored in the memory device (26) areupdated or adaptively adjusted so that continuous or long-term changesin the brake system are taken into account in the reference values. 5.The parking brake system as claimed in claim 1, wherein the controldevice (18) is supplied, as input variable, with signals for the forcewhich is to be exerted on the control cable (14), a force pickup (32)which is coupled to the brake pedal of the vehicle being used assetpoint value signal transmitter.
 6. The parking brake system asclaimed in claim 1, wherein the control device (18) is supplied, assetpoint value signal transmitter, with signals of an inclination sensor(34).
 7. The parking brake system as claimed in claim 1, wherein apotentiometer, the activation period of a momentary-contact switch, arocker or the like, is used as setpoint value signal transmitter.
 8. Theparking brake system as claimed in claim 1, wherein the actuator unit(12) is designed as a d.c. motor with connected or integrated gearmechanism (36).
 9. The parking brake system as claimed in claim 1,herein a travel value of the control cable (14) which is necessary toexert a redetermined force value during the process of pulling on thebrake is stored in the memory device (26), and the control cable (14) ismoved by a preferably constant travel value by means of the actuatorunit (12) in order to release the brake.
 10. The parking brake system asclaimed in claim 1, wherein a display device (38),such as a visualdisplay, for example an LED array or an audible indicator, with which acurrent brake force values can be represented, is connected to an outputof the control device (18).
 11. The parking brake system as claimed inclaim 1, wherein the operator device (20) is designed as a single-stage,multistage or stageless signal transmitter (40).
 12. The parking brakesystem as claimed in claim 1, wherein the operator device (20) isdesigned as a mechanical operator element (42) for pulling on orreleasing the control cable (14).
 13. The parking brake system asclaimed in claim 1, wherein, in the event of a service brake systemfailing, an auxiliary braking device (46) is provided for switching overthe parking brake system into an auxiliary braking mode, if appropriatea pedal (44) preferably the brake pedal, having a force pickup (32) assetpoint value signal transmitter for the parking brake system and/orthe braking force which is to be set, or an additional control unitand/or an additional actuator unit (12) and/or an additional batterybeing provided.
 14. The parking brake system as claimed in claim 1,wherein the control device (18) is supplied, as input variable, with atleast one of the following signals: signal from a ignition switch (48),signal from a immobilizer device (50), signal from a speed meter (52),signal from a brake light switch (54), signal from a antilock brakesystem (56), signals from a door lock contact (58), signals from adiagnostic device (60).
 15. The parking brake system as claimed in claim1, wherein, in the event of a fault being diagnosed in a service brakesystem of the vehicle, the parking brake system (10) is automaticallychanged over from an auxiliary braking device (46) into an auxiliarybraking mode.
 16. The parking brake system as claimed in claim 1,wherein the force which is exerted on the control cable (14) by theactuator unit (12) is limited to an upper limiting value by means of alimiting device (62).
 17. The parking brake system as claimed in claim1, wherein, in order to diagnose one of a fault, a motor current of theactuator unit(12), a duration of a braking procedure and the time bywhich the prescribed duration of the braking procedure is exceeded aremeasured.
 18. The parking brake system as claimed in claim 1, whereinthe activation of the actuator unit (12) takes place under servocontrol.19. The parking brake system as claimed in claim 18, wherein the servocontrol is carried out by means of pulse width modulation, by regulatingthe amplitude of one of a motor voltage, by means of clocked motorvoltage with constant mark-to-space ratio, and a by on-off operation ofa motor of the actuator device (12).